This invention relates to rotary mechanisms such as rotary engines, pumps, compressors, expanders, or the like.
Prior art of possible relevance includes U.S. Pat. No. 3,764,239.
Rotary mechanisms of the type having rotors mounted for rotation and translation within a chamber can be categorized into two types. In one type, the housing wall will have one or more lobes each having a relatively sharp transition point. An example of this type of mechanism is a hypotrochoidal mechanism of the type disclosed in U.S. Pat. No. 3,323,498 issued June 6, 1967 to Kraic et al.
The other group consists of such mechanisms wherein one or more lobes do not have sharp transition points, that is, the curves at the lobes are continuous with relatively generous radii. A typical mechanism in this category is a so-called "Wankel", or epitrochoidal mechanism, or a so-called "Clarke" mechanism, sometimes known as a slant axis rotary mechanism. The present invention concerns itself with the latter category of rotary mechanisms.
In such mechanisms, long life has been a long sought goal. The principal difficulty in achieving the goal has been the inability to provide long lived seals, particularly apex seals on the rotor. In designing such mechanisms, the housing geometry normally includes one or more lobes which are in the form of continuous curves having generous radii and such geometry is determinative of rotor shape with the result that the rotors have rather sharp apexes and very narrow apex seals.
For example, the method of housing design employed today is generally that of the above identified U.S. Pat. No. 3,764,239, wherein the housing geometry is not a true epitrochoid but rather, is a closed geometric figure or shape spaced outwardly of a true epitrochoid and parallel thereto. The spacing is selected to be equal to the radius of the curved sealing portion of the apex seal. Such a design provides larger seals than would be possible if the housing followed the shape of a true epitrochoid, but even so, in the typical Wankel engine in commerical use today, sealing contact between an apex seal and the housing shifts no more than about 0.05 inches on the surface of the apex seal. The confinement of sealing contact to such a small area causes rapid wear, even when exotic materials are employed in forming the seals.
As far as is known, no consideration has been given to larger seals in such mechanisms, which larger seals would require the actual housing geometry to be spaced an even greater distance from the true epitrochoid on which the design is based. The use of larger radius seals would increase the distance over which sealing contact between an apex seal and the housing shifts to decrease the wear rate on any given part of the sealing surface to thereby provide longer life.
The apparent failure to consider such seals may be due principally to two factors. The first is inertia loading on the seals. Increasing the radius of the sealing surface of state of the art seals would significantly increase their mass, resulting in greater inertia forces during operation of the mechanism in which they are used if the apex seals are disposed in grooves which extend radially of the rotor, as is the case with an epitrochoidal mechanism, thereby increasing frictional forces and increasing the wear rate due to such inertia loading.
A second probable factor is the fact that as the housing shape is removed further and further from the true epitrochoid, as required by the increased radius of the seals, the housing geometry at the lobes changes from continuous curves having generous radii to abrupt curves having sharp transition points which may be in the form of either discontinuous curves or in the form of continuous curves having extremely small radii. As a consequence, high contact stresses would be present at the lobes so that the lubricating oil film would be virtually nonexistant. As a result, friction would be high and the temperature of the rubbing surface at the contact point (the conjunction temperature) would also be undesirably high, causing scuffing and rapid wear of the housing.